: What you say about the epoxy shrinking as it cures is true, but
: that does not mean that humidity has no effect.

: I have only ever seen the curing epoxy cause small changes, but I
: have seen enormous changes caused by humidity variations even
: after the epoxy had cured for several weeks. I had a small flat
: panel about a foot wide curve up almost an inch in the middle
: when we had a few days of rain, then it returned to completely
: flat by itself when the sunny weather returned.

: Regardless of what causes the curling, spreader sticks can save a
: lot of struggling to get things to match later.

It's taken me a lot of years to realize just how great an effect increasing or, decreasing
humidity, has on wood strip construction. When one surface is glassed it is essentially "frozen"
and the bare wood surface will expand, with increased moisture, and contract as it dries.

The amount of expansion and contraction will be most evident if there has been a long period of time
between when one surface is glassed and when the other surface is glassed.

Building here in the north in the winter, humidity levels are constantly dropping.
I work with the assumption that when I'm ready to glass the inside of my hull and deck,
the bare wood interior surfaces will have shrunk, and I must soak them down with a
wet sponge before I glass, to expand the interior surfaces back to where they were when
I glassed the exterior.

It is routine for me to set-up a series of spacer sticks along the length of the hull and deck
to ensure they are the proper dimensions after the interior glass has cured.

If you wish to see the effects of changing humidity levels for yourself, make a strip panel,
glass one surface and cut a 3/4" wide strip ACROSS the wood grain. Tack it to an outdoor window
frame, so it sticks out perpendicular to the wall. That baby will wiggle like an inchworm with
changing weather!

It's part of the physics of wood, there's no getting around it. Understand it and use it to
your advantage. If your wood is exposed to increasing moisture it will expand, if humidity
is dropping it will contract. The greatest effect will be across the wood grain.

However, there IS enough of an effect on wood length to cause stems to be pushed out of alignment
if strips are applied to only one side of a hull. Therefore, it is best to apply no more than four strips
to one side of your hull, before applying an equal amount to the other side.

The effects of moisture are most dramatic with thin sections of wood, like the strips we use.

So, if one surface is glassed and "frozen" and the interior bare wood has shrunk, wet the surface to
expand it back to where is was. If the interior bare wood has expanded, dry it, (heat gun) to contract it
back to were it started.

Rob

I hear, I forget. I see, I remember. I do, I understand.

Confucius